Question

所以说我有一个像这样的mysql语句：

  SELECT username, @n := @n + 1 ranking, `1st places`, `2nd places`, `3rd places`, `top5`, `top3
FROM
(
SELECT username,
SUM(CASE WHEN rating = 1 THEN 1 ELSE 0 END) `1st places`,
SUM(CASE WHEN rating = 2 THEN 1 ELSE 0 END) `2nd places`,
SUM(CASE WHEN rating = 3 THEN 1 ELSE 0 END) `3rd places`,
SUM(CASE WHEN rating < 6 THEN 5 ELSE 0 END) `top5`,
SUM(CASE WHEN rating < 4 THEN 5 ELSE 0 END) `top3`
FROM Table1
GROUP BY username
ORDER BY `1st places` DESC
) q, (SELECT @n := 0) n

如何在这个sql语句中添加我创建的名为'1st places'+'2nd places'+'3rd places'的列，并创建另一个名为“total finish”的列？看起来很简单，但我似乎无法弄明白。

Answer 1

您可以将它们添加到一起，并为该额外列提供别名： -

SELECT username, @n := @n + 1 ranking, `1st places`, `2nd places`, `3rd places`, `top5`, `top3, `1st places` + `2nd places` + `3rd places` AS `total finishes`
FROM
(
SELECT username,
SUM(CASE WHEN rating = 1 THEN 1 ELSE 0 END) `1st places`,
SUM(CASE WHEN rating = 2 THEN 1 ELSE 0 END) `2nd places`,
SUM(CASE WHEN rating = 3 THEN 1 ELSE 0 END) `3rd places`,
SUM(CASE WHEN rating < 6 THEN 5 ELSE 0 END) `top5`,
SUM(CASE WHEN rating < 4 THEN 5 ELSE 0 END) `top3`
FROM Table1
GROUP BY username
ORDER BY `1st places` DESC
) q, (SELECT @n := 0) n

Answer 2

我很确定您无法在同一SELECT查询中重复使用具有计算值的字段，但是可以选择包装到其他子查询中：

SELECT username, @n := @n + 1 ranking, `1st places`, `2nd places`, `3rd places`, `top5`, `top3
FROM
(
    SELECT
    *,
    `1st places`+`2nd places`+`3rd places` `total finishes`
    FROM (
        SELECT username,
        SUM(CASE WHEN rating = 1 THEN 1 ELSE 0 END) `1st places`,
        SUM(CASE WHEN rating = 2 THEN 1 ELSE 0 END) `2nd places`,
        SUM(CASE WHEN rating = 3 THEN 1 ELSE 0 END) `3rd places`,
        SUM(CASE WHEN rating < 6 THEN 5 ELSE 0 END) `top5`,
        SUM(CASE WHEN rating < 4 THEN 5 ELSE 0 END) `top3`
        FROM Table1
        GROUP BY username
        ORDER BY `1st places` DESC
    )
)
q, (SELECT @n := 0) n

还没试过，还是......

添加你在mysql中创建的列？

2 个答案: